He needed five hours and 14 minutes of play to conquer his opponent on Tuesday.
When asked how his arm felt after functioning like an artillery gun, he said: "Arm is good. But my knee, my back not so good. All in all, the elbow is okay. Everyday it's like this."
When queried about where he found the energy to last out the five setter, serving 75 aces, he said: "I don't know. Gatorade and water, I guess. I began really bad. I didn't really feel so good on court. I was just trying to hang in there point by point."
"I don't know how I will recover from this match. I have two days off. Hopefully that will be enough."
Karlovic has one of the mightiest serves on the men's tennis tour. His booming serves, his main weapon, often land top players into trouble.
In the Australian Open so far, Karlovic leads with a 69 percent serve success rate while his first round opponent Zebellos has an admirable 61 percent rate above all the top-ranked players.
Despite his formidable serve, Karlovic hasn't been able to reach the title rounds of tournaments, probably lacking in court craft and not being as fast as a top singles player should be.
His opponents find it easy to make him run from one corner to the other of a court. Karlovic is now ranked 20 and if he continues his barrage of serves he may end up bruising a lot of top stars.